There is a known particle forming process called Stop-Flow-Lithography which uses microfluidic channels and a system interface that allows starting and stopping the flow at specific times. The fluid typically contains a precursor (e.g. PEG-DA) and a photoinitiator. When the channel is filled with the solution, the flow is stopped, and a microscope objective projects a pattern of ultraviolet (UV) light into the channels to initiate local polymerization. This creates a two-dimensional (2D) shaped bulk of crosslinked polymer that becomes the particle. After polymerization, the flow is restarted, the particles are flushed out and replaced by new precursor, and the next particle is synthesized. In this Stop-Flow-Lithography technique, the creeping flow at finite Reynolds numbers, which is typical for microfluidic channels, allows leveraging properties, such as diffusion based mixing, to create arbitrary, anisotropic 2D particles with stripes or internal gradients of various properties like fluorescent dyes or controlled concentration of colloid particles.
However, it is difficult to scale the Stop-Flow-Lithography technique to an industrial setting because it relies on closed micro-channels and single microscope objectives per channel. Further, particles tend to stick to the top and bottom channel walls during polymerization. This limits its use as a continuous process.
Also, microlens arrays have been used for projection lithography, most notably in work relating to complex patterning of sub-micrometer features over large area surfaces using PDMS stamps with integrated glass microspheres as lenses.